1. Field of the Invention
The present invention relates to a liquid ink and a recording apparatus. In particular, the present invention relates to an ink for an ink jet and to an ink jet recording apparatus.
2. Description of the Related Art
In a situation where a fairly large number of copies of printed matter are required such as in the cases of printing copies of local advertisement bill and enterprise handout, a printing machine utilizing a form plate has been conventionally employed for meeting such requirements. In recent years however, an on-demand printer which is capable of quickly coping with the diversification of needs and of minimizing stocks has been increasingly utilized in place of the aforementioned conventional printing machine. As for such an on-demand printer, an ink jet printer is expected to be useful as the ink jet printer is capable of achieving high-speed and high-quality printing.
With a view to achieve the printing of highly brilliant images by using an on-demand printer, there is known a technique to employ a solvent type ink or a solvent type liquid toner both containing a pigment and an organic solvent in the same manner as in the case of a printing machine utilizing a form plate. This technique however leads to the evaporation of organic solvent to such an extent that cannot be disregarded when the printing is repeated a certain number of times. Therefore, when this technique is employed, a problem of environmental contamination due to this evaporated organic solvent will be raised, thus necessitating the provision of an exhaust gas processing installation or a solvent recovery system.
Under the circumstances, a photosensitive ink and a printer system employing the photosensitive ink are now taken notice of as a technique which is effective in overcoming the aforementioned problem. In this technique, the photosensitive ink that has been migrated to the surface of printed matter photo-cures quickly. As for the photosensitive ink employed therein, the typical example comprises, as indispensable components, a radical polymeric monomer, a photopolymerization initiator and a pigment.
Since an ink layer formed of such a photosensitive ink can be readily nonfluidized by irradiation with light, it is possible, with the employment of this printing system, to obtain printed matter of relatively high quality. However, the ink employed therein contains a large quantity of carcinogens such as a radical-generating agent, and moreover, a volatile acrylic derivative employed as a radical polymeric monomer is highly skin-irritating and bad smelling. Namely, this photosensitive ink is required to be treated carefully. Further, the radical polymerization in the ink is obstructed greatly by the presence of oxygen in the atmosphere and at the same time, the exposure light is absorbed by the pigment included in the ink. Therefore, the dosage of exposure tends to become insufficient at a deep region of the layer of ink. As a result, the sensitivity of this photo-sensitive ink to the exposure light is relatively low so that a considerably sophisticated exposure system would be required in order to obtain printed matter of high quality in the employment of this printer system.
With a view to overcome these problems, there has been proposed a cationic curing type ink which cure through irradiation with an active energy beam. This cationic curing type ink can be employed in such a manner that it is discharged from an ink jet print head for instance to form a pattern of ink layer corresponding to a desired image on a recording medium and then, the resultant ink layer is subjected to irradiation with active energy such as ultraviolet rays or an electron beam to cure the ink layer.
However, there is a problem common to all kinds of photo-cationic curing type inks for an ink jet that the viscosity of the ink fluctuates considerably with time. The reason for this can be attributed to the fact that the ink is quite vulnerable to dark reaction. When the viscosity of ink fluctuates, the trajectory of ink would be disordered and the reproducibility of printing would be badly affected in the case of the ink for an ink jet in particular. In the worst case, critical situations such as discharge failure or clogging of ink would be caused to occur. Therefore, the fluctuation in viscosity of ink is one of very serious problems. No one has succeeded as yet to find an effective measure to solve this problem of increase in viscosity of the ink for an ink jet.
Photo-cationic curing type inks for ink-jet containing an oxirane group-containing compound, an oxetane ring-containing compound, a vinylether compound, a pigment, a pigment-dispersing agent, photo-acid generating agent and other additives are liable to indicate a great magnitude of fluctuation in viscosity (increase in viscosity) with time due to the dark reaction of the inks for an ink jet which would take place quite prominently. Therefore, the photo-cationic curing type inks for an ink jet are poor in shelf life and hence short in useful life.